Nondestructive testing of the fatigue properties of air plasma sprayed thermal barrier coatings by pulsed thermography¹

The fatigue properties of air plasma sprayed (APS) thermal barrier coatings (TBC) were investigated by quantitative Pulsed Thermography (PT). This analysis principally concerned with microstructural evolution during the thermal cyclic. The microstructural features of the specimens were examined by scanning electron microscopy (SEM). The TBC fatigue life was correlated with the development of the thermally grown oxide (TGO) and defects cracks. For better understanding of the thermal response from the surface of TBC, APS TBC samples were inspected as a function of ageing time by PT. The changes in the thermal response amplitude (TRA) were found to correlate with the TGO layer growth and crack nucleation, which was verified by SEM results. The experimental results demonstrated that the thermal response decreased correspondingly along with the increase of the TGO and cracks thickness. The relationships of TRA obtained from the surface of TBC samples with the thickness of TGO and cracks were established. A simple and effective method for quantitative measuring TGO layer and cracks thicknesses using the nondestructive testing of PT was proposed. The experimental results provide a basis for the application of PT in the nondestructive testing of the fatigue properties of TBC thermal fatigue.